Heterogeneous photocatalysis has attracted great interest for the degradation of toxic organic and inorganic species, inactivation of pathogenic microorganisms, and odor removal from contaminated environments. Photocatalysts currently used are mostly in the form of aqueous TiO2 slurries or suspensions. Some of the problems with TiO2 suspensions are the need for ultraviolet (UV) irradiation to activate the photocatalyst, and difficulty recycling the dispersed photocatalyst. To eliminate the requirement for UV irradiation, a few research groups have reported using visible light to induce photocatalysis of metal or nonmetal element doped TiO2 (1-7). Metal and nonmetal element co-doped TiO2 often exhibits improved photocatalytic activity compared to single element doped TiO2, under visible light irradiation (8-10, 31, 32).
For easy recycling of photocatalysts, a variety of systems using immobilized titania on metallic or nonmetallic supports (11), glass (12), polymer substrate (13) and activated carbon fibers (10) have been proposed. For application on an industrial scale, the immobilized photocatalyst faces a new problem: the reaction efficiency is often restricted by the limited contact area of the immobilized photocatalyst. A few efficient dynamic photoreactors have been reported for UV irradiated TiO2 systems which may be the useful for studying visible light activated photocatalysts (14, 15). Choi and Kim conducted photocatalytic disinfection in a plug-flow type photobioreactor using optical fibers inserted in glass tubes (16). The optical fibers were used to diffuse the UV light uniformly within the reactor. Shchukin et al. studied heterogeneous photocatalysis in a titania-containing liquid (17).